On Sat, 15 Jan 2005 11:03:46 -0500, "Phil Kangas"
wrote:

Here's an interesting site concerning the experiments
done with plumb lines in the Tamarack Mine near
Calumet Michigan in 1901. This has been recognized
by the Guiness Book of world records just lately.
Metal content : this is a copper mine...............
Phil Kangas

http://www.lhup.edu/~dsimanek/hollow/tamarack.htm

Fascinating!